Tests: Control testing fileserver from plugin tests, not other tools running the tests

Currently paramedic includes code to install and control the file server that is needed for these tests here to succeed: https://github.com/apache/cordova-paramedic/blob/ff6b2fa00b2e5b11907f2e7d0296f7b35feb4a04/lib/LocalServer.js#L78-L112 This code should live here, not with paramedic, so the testing also works outside the context of paramedic.

Start by reviewing the referenced LocalServer.js section in cordova-paramedic, especially the code that installs and controls the file server. Trace how cordova-plugin-file-transfer tests currently rely on that setup, then move the responsibility into the plugin tests so they run successfully outside paramedic.

Written by the indexing model from the issue text.